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Clarify portability pitfall of test.

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* doc/autoconf.texi (Limitations of Builtins) <test>: Give more
reasons why -a and -o are not portable.
Reported by Reuben Thomas.

Signed-off-by: Eric Blake <ebb9@byu.net>
This commit is contained in:
Eric Blake 2009-09-10 20:05:21 -06:00
parent 9c16f1a80d
commit 98410813c9
2 changed files with 19 additions and 6 deletions
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@ -1,3 +1,10 @@
2009-09-10 Eric Blake <ebb9@byu.net>
Clarify portability pitfall of test.
* doc/autoconf.texi (Limitations of Builtins) <test>: Give more
reasons why -a and -o are not portable.
Reported by Reuben Thomas.
2009-09-10 Ralf Wildenhues <Ralf.Wildenhues@gmx.de>
Document sed limitation with escaped metacharacters.

18
doc/autoconf.texi
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@ -16388,12 +16388,18 @@ that name in Autoconf code is asking for trouble since it is an M4 quote
character.
The @option{-a}, @option{-o}, @samp{(}, and @samp{)} operands are not
portable and should be avoided. Thus, portable uses of @command{test}
should never have more than four arguments, and scripts should use shell
constructs like @samp{&&} and @samp{||} instead. If you combine
@samp{&&} and @samp{||} in the same statement, keep in mind that they
have equal precedence, so it is often better to parenthesize even when
this is redundant. For example:
present in all implementations, and have been marked obsolete by Posix
2008. This is because there are inherent ambiguities in using them.
For example, @samp{test "$1" -a "$2"} looks like a binary operator to
check whether two strings are both non-empty, but if @samp{$1} is the
literal @samp{!}, then some implementations of @command{test} treat it
as a negation of the unary operator @option{-a}.
Thus, portable uses of @command{test} should never have more than four
arguments, and scripts should use shell constructs like @samp{&&} and
@samp{||} instead. If you combine @samp{&&} and @samp{||} in the same
statement, keep in mind that they have equal precedence, so it is often
better to parenthesize even when this is redundant. For example:
@smallexample
# Not portable: